This paper presents a framework for evaluating and accounting for the outcomes of ‘greenfield’ union organizing campaigns. It argues that previous studies have tended to focus too much on the establishment of collective bargaining and negotiation of first contract as a campaign outcome. Instead, the effectiveness and representativeness of new union structures are emphasized, and the sustainability of those structures is emphasized as the most important outcome. A key finding from the empirical data is that campaigns that build both workplace activism and are co-ordinated by officers create more sustainable outcomes than campaigns that focus on one or the other. The evidence shows how and why these outcomes emerge, and the paper concludes with a consideration of the theoretical and practical implications.